


A Thin Line

by SmoleWritey



Category: Shingeki no Kyojin | Attack on Titan
Genre: 104th Training Corps Shenanigans, Armin does not understand sexual tension, Attempt at Humor, Comedy of Errors, Eren Yeager Being an Idiot, F/F, Humor, Mild Sexual Content, Misunderstandings, POV Armin Arlert, Top Mikasa Ackerman, Unreliable Narrator
Language: English
Status: Completed
Published: 2021-02-22
Updated: 2021-02-22
Packaged: 2021-03-12 17:20:16
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,100
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29637993
Author URL: https://archiveofourown.org/users/SmoleWritey/pseuds/SmoleWritey
Summary: Armin can’t figure out why Mikasa and Annie hate each other. In fact, he’s pretty sure they’ve never even spoken. Just what in the hell is going on?
Relationships: Mikasa Ackerman/Annie Leonhart
Comments: 11
Kudos: 151





	A Thin Line

**Author's Note:**

> Me: Lovingly crafts the plot for a multi-chapter fic, only to never actually start writing it.  
> Also me: Has a completely silly idea with no plot or plan and has to write it immediately.
> 
> Why am I like this?

If you asked Armin, there was entirely too much animosity within the 104th cadet corps.

For starters, there was the ridiculous rivalry between Eren and Jean, which had tempers flaring hot almost as soon as they had enlisted. Of course, Eren had a special talent for bullishly picking fights, so Armin wasn’t exactly surprised. Still, how did they have enough energy to hate each other that much at all hours, day in and day out? You’d think they would be too worn out after each day’s brutal training, but somehow, several times a week, one of the boys would be unable to hold back a snide comment and they would come to blows in the middle of the mess hall. Thankfully, Mikasa always sprung up from her seat in time to either forcibly separate them, or if it had been a particularly trying day, just knock them both out cold so she could finish her meal in peace.

Then there was Ymir. Not that Ymir had a grudge against anyone in particular. No, it was more like she had a grudge against… _everyone_ in particular. As if the world at large had personally insulted her. She was unforgivingly harsh and unthinkingly blunt and in her short time in the cadets, had ruffled feathers with such ease that she rivaled Eren. In fact, the only person she almost got along with was Christa, and even this special status didn’t exempt the poor girl from Ymir’s biting remarks.

But most worrying – and surprising – was the slowly escalating standoff between Mikasa and Annie. Mikasa was supposed to be the logical, level-headed one in their little trio, but it seemed that whatever was in the water that had everyone on edge had gotten to her too. Armin could find no logical explanation for why Mikasa seemed to loathe Annie on sight, and so he had no idea how to help the situation. Worse, he was pretty sure that no one else had even noticed. Armin was alone in watching this dangerous game play out.

Seemingly, it had all started when they first joined the Cadet Corps, even before they had a chance to properly met the other recruits. Armin was walking outside the cabins with his two best friends, listening to Eren whisper excitedly about being closer than ever to his dream of joining the Survey Corps. As always, Eren got himself worked up, talking about killing all the Titans and freeing humanity, his eyes flashing with cold rage, the whole nine yards. Usually, when this happened, Mikasa would scold some sense into Eren and bring him back to reality, but this time when Armin looked to her… she wasn’t there anymore. Armin blinked, looking around.

Several paces behind them, Mikasa stood frozen. Her face was impassive as ever, but Armin thought he saw something stormy stirring in her eyes. He followed her gaze across the yard to a petite blond girl leaning against the edge of the well, arms crossed, with a bored expression on her face. She wore her hair tied back in a bun with her bangs shielding her eyes on either side. Despite her small stature, something about her, maybe her calculating gaze, or her standoffish posture, indicated that she was not someone to be trifled with.

Armin opened his mouth to call to Mikasa, but at that moment, the girl lifted her head and spotted Mikasa. Armin fell silent. The seconds stretched on as the two stared coolly at each other, unmoving.

In the depths of Mikasa’s dark eyes, the strange storm brewed. A cold wind whipped through the girls’ hair, bringing movement to the otherwise still scene. Suddenly, the blonde’s face twisted out of its mask into a deep scowl. She jutted her chin out proudly in what appeared to be a challenge.

Armin’s mouth dropped open. What was _happening_? Not a word had been exchanged yet. Did this girl know Mikasa somehow? Armin was sure he would know if his friend had run afoul of someone, they had been together almost constantly since leaving Shiganshina. None of this was making sense.

The storm in Mikasa’s eyes flashed like lightning. Slowly, she bared her teeth in a feral smile, rising to the bait.

Armin held his breath.

“Armin! Mikasa!”

Armin startled so badly he almost fell over. Eren was gesturing at them impatiently.

“Like I was saying! I want to get a look at the training grounds, so I know what to expect. We can get a head start on the other recruits. Are you coming?”

When Armin looked back at Mikasa, she was already striding towards them as if nothing had happened, her expression smoothed over. “Yes, let’s go.”

As Armin turned to follow, he didn’t miss how the blonde’s eyes bore into Mikasa’s back as they retreated.

Weeks later, amid all their training, Armin might very well have forgotten about the incident, if not for the fact that it _just kept happening_.

During weapons training. During combat drills. During lectures. During breaks.

During meals, like right now, ruining what should have been a peaceful dinner.

The two girls would lock eyes for seconds at a time, doing nothing but glaring at each other, Annie’s stare cold and piercing against Mikasa’s intense heat, their faces betraying nothing. This exchange was done so subtly that Armin was sure it was only because of his uniquely perceptive nature and the fact that he had witnessed their bizarre first interaction that he had picked up on their mutual hatred at all. And now that he had noticed, he couldn’t help noticing it _all the time_ , leaving him practically itching out of his skin.

There was no telling when this mess would come to a breaking point. Mikasa was an expert at keeping her emotions under control, but on the rare occasion they flared up, the result was sharp and deadly. Not to mention, from what he had seen in their time as trainees, Annie was a force of nature in her own right. If the two decided to fight it out… Armin paled at the thought. He could not let that happen.

Despite signing on to become a soldier, he was a peacemaker at heart. He hated conflict and believed in his responsibility and capability to resolve it as often as he could. After years of friendship, he had given up Eren as a lost cause. But Mikasa could be relied on to keep a level head. As much as she intimidated him sometimes, he could still try to broach the subject.

Yes, Armin decided, he would talk to the raven-haired girl tonight. He would ask her what was going on, he would help her extend an olive branch to Annie, the two would settle any misunderstandings between them, and the Cadet Corps could move on from one neatly averted crisis. All in a day’s work for a burgeoning young strategist.

Satisfied, he turned his attention back to the soup in front of him. He let the warm liquid melt away the stress of the day as it slid down his throat and settled in his belly. Surrounded by the idle chatter of his fellow trainees as they ate and wound down for the day, he lost himself in a rare moment of contentment.

Of course, like most nice things in this world, it was not to last.

Armin tuned in to the world around him just in time to hear the tail end of Eren’s conversation with Reiner.

“…and that’s why the Military Police are a complete waste of resources,” Eren finished, raising his voice considerably at the end. Armin groaned softly.

From the other side of the room, Jean slammed his hands down flat on his table, springing to his feet.

“You still trying to pick a fight, Jeager?” He bellowed.

Eren copied the motion almost exactly, whirling to face his challenger.

“I don’t know, you still a whiny bitch, Kirstein?”

God. Where was Mikasa when you needed her?

No, seriously, where was she? She had been seated right by Armin a minute ago.

Armin searched the room desperately. There. While everyone was distracted by the two obnoxious boys and their pissing contest, Mikasa had taken the opportunity to silently slip out the door to the mess hall. Armin noticed Annie seated a few tables away, watching her leave. As soon as the door closed, the blonde girl stood smoothly, depositing her bowl, and disappeared after her.

Armin looked back and forth between the closing door and the scene in front of him. Jean had thrust his arms out in front of him to push Eren backwards. Eren stumbled. The door fell closed.

Eren and Jean were always stupid enough to pick a fight in plain sight. Surely, one of the other recruits would alert Shaadis. Mikasa and Annie were more dangerous. Armin had no idea what they were up to, and no one else could stop them from what he was convinced would end in mutual annihilation. It was up to him.

His decision made, Armin stood up abruptly from his seat and pursued the pair into the chilly night. The lamps that hung outside provided minimal light, and he saw the silhouette of Annie disappearing in the distance in purposeful strides. Armin did his best to tail her silently, but lost sight of her. He could barely see a thing in the encroaching darkness. A muffled thud followed by a crash echoed from the direction of the storehouse. _Shit, that sounds bad._ Armin winced and followed the sound blindly.

Stumbling through the night, he huffed to himself and wrapped his cloak tighter around him. It struck him that he was on his way – alone – to break up a fight between frankly the two scariest cadets in the entire regiment. He shivered, not entirely from the cold, and not for the first time in the past few months, questioned all his life choices.

As he approached, he heard another muffled thud and a grunt of pain, sparking his sense of urgency. One of the doors to the building was cracked open, and Armin raced inside. In the dim lighting, next to the grain stores, he spotted Mikasa and Annie grappling against the wall. Mikasa appeared to have pinned Annie back with an arm across her throat, towering over the shorter girl.

Someone was going to get hurt here. Armin had to put a stop to this.

He had just rushed forward, ready to shout at them, when Annie suddenly let out a breathy moan.

_Wait, what?_

They shifted slightly, and as Armin’s eyes adjusted to the light, his brain caught up to the sight in front of him, bringing his thoughts stuttering to a halt.

Mikasa and Annie were _not_ fighting.

Indeed, Mikasa had Annie pinned against the wall roughly, crowding against her. However, she also had the other hand slipped under Annie’s shirt and moving purposefully, one knee slotted between Annie’s thighs, grinding slowly. Her fiery black eyes were locked in a dance with Annie’s icy blue, burning together.

Embarrassed heat rushed to Armin’s cheeks so fast he felt dizzy, his mouth gaping. That look he had been noticing for weeks… was not a glare at all? He did not see this coming. As Mikasa leaned in to capture Annie’s mouth with her own and moved her hand down to undo Annie’s pants, Armin snapped back to his senses. He turned and ran faster than he had in his life, faster even than when he escaped Shiganshina. He thanked whatever gods there might be for the small mercy that the girls had apparently been too wrapped up in each other to notice his momentary intrusion.

A safe distance away, he rested his hands on his knees, gasping for breath.

Mikasa and Annie?!? When did that even happen? Did this mean they didn’t hate each other after all?? Armin couldn’t figure out how he had read the situation so wrong. He put his head in his hands. This was all so far above his pay grade. Mikasa and Annie could handle themselves, he decided, and he no longer wanted anything to do with it.

Briefly, he wondered if he should go back to the mess hall to make sure someone had deescalated the fight between Eren and Jean. He paused, wide-eyed. Surely, _those two_ weren’t actually… having relations too?

He shook himself. No, better to cut his losses now and let anyone else take care of it. The conflicts of the world could wait until tomorrow.

Armin was going to bed.

Surely, he had earned it.

**Author's Note:**

> Haha, what a mess xD  
> If you like my writing, Attack on Titan in general, or women who could kill you with a glance, follow me on [Twitter](https://twitter.com/SmoleWritey)!


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